Siemens SIPROTEC 7SD610 Manual page 87

Figure 2-32
It is also possible to increase the tripping value proportional to the current sum. In this case the pickup value is
stabilized with the arithmetic sum of all currents, i.e. with „IrestREF=" Σ | I | = | I
The slope of the characteristic curve can be adjusted.
Pickup
Normally, a differential protection does not need a „pickup", since the fault detection and the trip condition are
identical. But the earth fault differential protection, like all protection functions, has a pickup function which is
required for tripping and serves as the starting point for a number of further activities.
As soon as the fundamental component of the differential current reaches approximately 85 % of the pickup
value, pickup is recognized. In this aspect, the differential current is represented by the sum of all in-flowing
currents.
Figure 2-33
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011
Tripping characteristic of the restricted earth fault protection in dependence on the phase dis-
placement between 3I " and 3I
0
Increasing the pickup value
2.5 Restricted Earth Fault Protection (optional)
o
' at 3I " = 3I ' (180 = external fault)
0 0 0
Functions
| + | I | + | I | + | I |.
L1 L2 L3 4
87